Invading 3-3
For most of Go's history, invading at 3-3 early was considered too small: you'd grab the corner but be sealed in, giving the opponent imposing outside thickness. AlphaGo and its successors overturned that. In the AI era, the 3-3 invasion under a 4-4 stone — often as the fifth or sixth move — is one of the most common professional opening sequences. The lesson: thickness is valuable, but so is concrete territory, and the trade is fair.